1. Field of the Invention
The use of calcium aluminate clinker as a refractory aggregate in shapes and castables is covered under a separate filing. This filing addresses the use of calcium aluminate clinker as a dry fill material or as a castable or a combination of both (product) used to provide insulation and degree of chemical protection via reaction with certain materials present in the pot salt bath associated with primary aluminum production. The present invention provides an improved refractory aggregate based on Ca0•Al203 clinker (hereinafter referred to as “CA” clinker and designated by the following equation CnAx, wherein preferably n is an integer from about 1 to 12 and x is an integer from about 1-24) and CnAx hydrate phases and analogs or derivatives thereof including those based on barium substitution for calcium or barium additions resulting in calcium substitution after chemical reaction and/or heat treatment, all of which are referred to herein as CA clinker. Refractory materials based on aggregate compositions having these phases singularly or combined, and exclusive of C12A7 as a major phase, are provided in the present invention.
2. Description of the Background Art
Lafarge Calcium Aluminates Inc. (Maryland, USA) markets a calcium aluminate clinker as an aggregate available under their “r50” trade name. This clinker known by those skilled in the art is about 52% alumina and is dense. The presence of a relatively large amount of C12A7 causes the LaFarge Calcium Aluminates, Inc.'s calcium aluminate clinker to melt and the product is essentially fused with little or no porosity. Thus, this composition has little utility as a refractory aggregate. In one embodiment of the present invention, a composition is provided that comprises a CnAx clinker that lacks significant amounts of C12A7 and that has the additional benefit of the presence of porosity and usefulness as a refractory aggregate. In addition, the proposed use of any CA material as a chemical trap for application in primary aluminum production is unique regardless of the ‘refractoriness’ of the material. Thus for this application CA in the form of C12A7 is also a viable chemical trap.
It is known in the refractory arts that the addition of barium-containing materials impart a penetration resistance to materials in contact with molten aluminum. In another embodiment of the present invention, compositions are provided wherein barium is substituted into the CA clinker matrix of the present invention resulting in BA6, BC2A4 and the other analogs that increase the performance of the product.
The primary area of application for the dry fill product of the present invention is as a backup/safety lining in aluminum pots. In this application the material provides protection from aluminum penetration, insulating character due to inherent thermal conductivity, and penetration by bath salts/fluxes that are used in the aluminum electrolysis process. While not desiring to be bound by any particular theory, the applicant believes that this last benefit is via chemical trapping (trapping of a material by reaction with another material).